#GEO600

[whats-in-a-sentence]

With LIGO and its subsequent improvements,* we will view the cosmos in a completely new way.

* One of these is the planned Laser Interferometer Space Antenna (LISA), a space-based version of LIGO comprising multiple spacecraft, separated by millions of kilometers, playing the role of LIGO's four-kilometer tubes. There are also other detectors that are playing a critical role in the search for gravitational waves, including the German-British detector GEO600, the French-Italian detector VIRGO, and the Japanese detector TAMA300.

"The Fabric of the Cosmos" - Brian Greene

[arxt1]

First joint observation by the underground gravitational-wave detector, KAGRA, with GEO600. (arXiv:2203.01270v1 [gr-qc])

We report the results of the first joint observation of the KAGRA detector with GEO600. KAGRA is a cryogenic and underground gravitational-wave detector consisting of a laser interferometer with three-kilometer arms, and located in Kamioka, Gifu, Japan. GEO600 is a British--German laser interferometer with 600 m arms, and located near Hannover, Germany. GEO600 and KAGRA performed a joint observing run from April 7 to 20, 2020. We present the results of the joint analysis of the GEO--KAGRA data for transient gravitational-wave signals, including the coalescence of neutron-star binaries and generic unmodeled transients. We also perform dedicated searches for binary coalescence signals and generic transients associated with gamma-ray burst events observed during the joint run. No gravitational-wave events were identified. We evaluate the minimum detectable amplitude for various types of transient signals and the spacetime volume for which the network is sensitive to binary neutron-star coalescences. We also place lower limits on the distances to the gamma-ray bursts analysed based on the non-detection of an associated gravitational-wave signal for several signal models, including binary coalescences. These analyses demonstrate the feasibility and utility of KAGRA as a member of the global gravitational-wave detector network.

from astro-ph.HE updates on arXiv.org https://ift.tt/C183zAi

[maxisama]

32. LAS ESTRELLAS: LOS AGUJEROS NEGROS.

32.1: AGUJEROS NEGROS. INTRODUCCIÓN.

Un agujero negro​ es una región finita del espacio en cuyo interior existe una concentración de masa lo suficientemente elevada y densa como para generar un campo gravitatorio tal que ninguna partícula material, ni siquiera la luz, puede escapar de ella. Sin embargo, los agujeros negros pueden ser capaces de emitir un tipo de radiación, la radiación de Hawking. conjeturada por Stephen Hawking en la década de 1970. La radiación emitida por agujeros negros como Cygnus X-1 no procede del propio agujero negro sino de su disco de acreción.

La gravedad de un agujero negro, o «curvatura del espacio-tiempo», provoca una singularidad envuelta por una superficie cerrada, llamada horizonte de sucesos. Esto es previsto por las ecuaciones del campo de Einstein. El horizonte de sucesos separa la región del agujero negro del resto del universo, y a partir de él ninguna partícula puede salir, incluyendo los fotones. Dicha curvatura es estudiada por la relatividad general, la que predijo la existencia de los agujeros negros y fue su primer indicio. En la década de 1970, Stephen Hawking, Ellis y Penrose demostraron varios teoremas importantes sobre la ocurrencia y geometría de los agujeros negros. Previamente, en 1963, Roy Kerr había demostrado que en un espacio-tiempo de cuatro dimensiones todos los agujeros negros debían tener una geometría cuasiesférica determinada por tres parámetros: su masa M, su carga eléctrica total e y su momento angular l.

Se conjetura que en el centro de la mayoría de las galaxias, entre ellas la Vía Láctea, hay agujeros negros supermasivos.

El 11 de febrero de 2016, las colaboraciones LIGO, Interferómetro Virgo y GEO600 anunciaron la primera detección de ondas gravitacionales, producidas por la fusión de dos agujeros negros a unos 410 millones de pársecs, megapársecs o Mpc, es decir, a unos 1337 millones de años luz, mega-años luz o Mal de la Tierra. Las observaciones demostraron la existencia de un sistema binario de agujeros negros de masa estelar y la primera observación de una fusión de dos agujeros negros de un sistema binario. Anteriormente, la existencia de agujeros negros estaba apoyada en observaciones astronómicas de forma indirecta, a través de la emisión de rayos X por estrellas binarias y galaxias activas.

La gravedad de un agujero negro puede atraer el gas que se encuentra a su alrededor, que se arremolina y calienta a temperaturas de hasta 12 000 000 °C, esto es, 2000 veces mayor temperatura que la de la superficie del Sol.

El 10 de abril de 2019, el consorcio internacional Telescopio del Horizonte de Sucesos presentó la primera imagen jamás capturada de un agujero negro supermasivo ubicado en el centro de la galaxia M87.

[monkeyandelf]

Is the universe a giant hologram?

A German scientist's experiment called GEO600 for the search for gravitational waves, which has been going on for seven years, has led to unexpected results, according to New Scientist.

Using a special device - an interferometer - physicists were going to scientifically confirm one of the conclusions of Einstein's theory of relativity. According to this theory, in the Universe there are so-called gravitational waves - perturbations of the gravitational field, “ripples” of the fabric of space-time. Propagating at the speed of light, gravitational waves presumably generate uneven mass movements of large astronomical objects: the formation or collision of black holes, a supernova explosion, etc. Science explains the unobservability of gravitational waves by the fact that gravitational effects are weaker than electromagnetic ones. Scientists who started their experiment back in 2002, intended to detect these gravitational waves, which could later become a source of valuable information about the so-called dark matter, which our Universe basically consists of. Until now, the GEO600 has not been able to detect gravitational waves, but, apparently, scientists using the device managed to make the largest discovery in the field of physics over the past half century. For many months, experts could not explain the nature of the strange noises that interfere with the operation of the interferometer, until suddenly an explanation was offered by a physicist from the Fermilab science laboratory. According to Craig Hogan’s assumption, the GEO600 faced the fundamental boundary of the space-time continuum — the point at which space-time ceases to be a continuous continuum described by Einstein and breaks up into “grains”, as if a photograph enlarged by a few turns into a cluster of individual points . “The GEO600 seems to have stumbled upon microscopic quantum vibrations of space-time,” suggested Hogan. If this information does not seem sensational enough to you, we’ll listen further: “If the GEO600 stumbles on what I suppose, it means that we live in a giant space hologram.” The very idea that we live in a hologram may seem absurd and absurd, but it is only a logical continuation of our understanding of the nature of black holes, based on a completely provable theoretical basis. Oddly enough, a “hologram theory” would essentially help physicists finally explain how the universe works at a fundamental level. The holograms we are used to (like, for example, on credit cards) are applied to a two-dimensional surface, which begins to seem three-dimensional when a light beam hits it at a certain angle. In the 1990s, Nobel Prize winner in physics Gerard Huft of Utrecht University (Netherlands) and Leonard Susskind of Stanford University (USA) suggested that a similar principle could be applied to the Universe as a whole. Our daily existence in itself can be a holographic projection of physical processes that occur in two-dimensional space. It is very difficult to believe in the “holographic principle” of the structure of the Universe: it is difficult to imagine that you wake up, brush your teeth, read newspapers or watch TV just because somewhere on the borders of the Universe several giant space objects collided. Nobody knows what “life in a hologram” will mean to us, but theoretical physicists have many reasons to believe that certain aspects of the holographic principles of the functioning of the Universe are reality. The findings of scientists are based on a fundamental study of the properties of black holes, which was carried out by the famous theoretical physicist Stephen Hawking together with Roger Penrose. In the mid-1970s, the scientist studied the fundamental laws that govern the universe and showed that Einstein's theory of relativity implies such a space-time that begins in the Big Bang and ends in black holes. These results indicate the need to combine the study of the theory of relativity with quantum theory. One of the consequences of such a union is the assertion that black holes are not really “black”: in fact, they emit radiation, which leads to their gradual evaporation and complete disappearance. Thus, a paradox called the “black hole information paradox” arises: the formed black hole loses mass, radiating energy. When a black hole disappears, all the information absorbed by it is lost. However, according to the laws of quantum physics, information cannot be completely lost. Hawking’s counterargument: the intensity of the gravitational fields of black holes is still inexplicably consistent with the laws of quantum physics. Hawking’s colleague, physicist Bekenstein, put forward an important hypothesis that helps resolve this paradox. He hypothesized that a black hole has entropy proportional to the surface area of ​​its conditional radius. This is a kind of theoretical area that masks a black hole and marks the point of non-return of matter or light. Theoretical physicists have proved that microscopic quantum oscillations of the conditional radius of a black hole can encode information inside a black hole, so that there is no loss of information inside a black hole when it evaporates and disappears. Thus, it can be assumed that three-dimensional information about the starting material can be completely encoded into the two-dimensional radius of the black hole formed after its death, approximately how a three-dimensional image of an object is encoded using a two-dimensional hologram. Zuskind and Huft went even further, applying this theory to the structure of the Universe, based on the fact that the cosmos also has a conditional radius - a boundary plane, beyond which light has not yet managed to penetrate over the 13.7 billion years of the existence of the Universe. Moreover, Juan Maldacena, a theoretical physicist at Princeton University, was able to prove that the same physical laws will act in a hypothetical five-dimensional Universe as in four-dimensional space. According to Hogan's theory, the holographic principle of the existence of the Universe radically changes the usual picture of space-time. Theoretical physicists have long believed that quantum effects can cause space-time to randomly pulsate on an insignificant scale. With this level of pulsation, the fabric of the space-time continuum becomes “grainy” and, as if made of the smallest particles, similar to pixels, is only hundreds of billions billion times smaller than the proton. This measure of length is known as the "Planck length" and is a figure of 10-35 m. At present, fundamental physical laws are verified empirically up to distances of 10-17, and the Planck length was considered unattainable until Hogan realized that the holographic principle changes everything. If the space-time continuum is a granular hologram, then the Universe can be represented as a sphere, the outer surface of which is covered with minute surfaces 10-35 m long, each of which carries a piece of information. The holographic principle states that the amount of information covering the outer part of the sphere-Universe must coincide with the number of bits of information contained within the three-dimensional Universe. Since the volume of the spherical Universe is much larger than its entire outer surface, the question arises, how is it possible to observe this principle? Hogan suggested that the bits of information that make up the "interior" of the universe should be larger than the Planck length. “In other words, the holographic universe is like a fuzzy picture,” says Hogan. For those who are looking for the smallest particles of space-time, this is good news. “In contrast to general expectations, the microscopic quantum structure is quite accessible for study,” said Hogan. While particles whose sizes are equal to the Planck length cannot be detected, the holographic projection of these “grains” is approximately 10-16 m. When the scientist made all these conclusions, he wondered whether it was possible to experimentally determine this holographic blurring of space. time. And then the GEO600 came to the rescue. Instruments like the GEO600, capable of detecting gravitational waves, work according to the following principle: if a gravitational wave passes through it, it will stretch the space in one direction and compress it in the other. To measure the wave, scientists direct the laser beam through a special mirror called the "beam splitter." It divides the laser beam into two beams that pass through the 600-meter perpendicular rods and come back. The rays that returned back are again united into one and create an interference picture of light and dark areas where light waves either disappear or reinforce each other. Any change in the position of these sections indicates that the relative length of the rods has changed. Experimentally, it is possible to detect changes in length less than the diameter of the proton. If the GEO600 really detected holographic noise from quantum oscillations of space-time, it will become a double-edged sword for researchers: on the one hand, noise will become an obstacle to their attempts to “catch” gravitational waves. On the other hand, this may mean that the researchers were able to make a much more fundamental discovery than originally thought. However, there is a certain irony of fate: a device designed to catch the waves resulting from the interaction of the largest astronomical objects, found something as microscopic as the "grains" of space-time. The longer scientists can not solve the mystery of holographic noise, the more acute the question arises of conducting further research in this direction. One of the possibilities for research may be the construction of the so-called atomic interferometer, the principle of operation of which is similar to GEO600, but instead of the laser beam, a low-temperature atomic flux will be used. What will the detection of holographic noise mean for humanity? Hogan is sure that humanity is one step away from discovering the quantum of time. “This is the smallest possible time interval: the Planck length divided by the speed of light,” says the scientist. However, most of all the possible discovery will help researchers trying to combine quantum mechanics and Einstein's gravitational theory. The most popular in the scientific world is string theory, which, scientists believe, will help describe everything that happens in the universe at a fundamental level. Hogan agrees that if holographic principles are proved, then no approach to the study of quantum gravity will henceforth be considered outside the context of holographic principles. On the contrary, this will be the impetus for the proofs of string theory and matrix theory. “Perhaps in our hands the first evidence of how space-time follows from quantum theory,” the scientist said. Read the full article

[fumpkins]

Four New Sources of Gravitational Waves

Space is moving: This numerical-relativistic simulation shows the very first observed combination of 2 black holes determined by the Advanced LIGO detectors on September 14,2015

© S. Ossokine, A. Buonanno (MaxPlanck Institut for Gravitational Physics, Simulating eXtreme Spacetimes Projekt, W. Benger (AirborneHydro Mapping GmbH)

Scientists have actually performed a better analysis of formerly tape-recorded information from the LIGO and Virgo gravitational wave detectors, locating four new signals. They all stem from the collison of sets ofblack holes Once once again, the scientists at the Max Planck Institute for Gravitational Physics in Potsdam and Hanover have actually made definitive contributions in essential locations to the observations and their analysis.

During the very first observing run O1, from September 12, 2015 to January 19, 2016, gravitational waves from 3 BBH mergers were spotted. The 2nd observing run, which lasted from November 30, 2016, to August 25, 2017, yielded a binary neutron star merger and 7 extra binary black hole mergers, consisting of the four new gravitational wave occasions being reported now. The new occasions are referred to as GW170729, GW170809, GW170818 and GW170823 based upon the dates on which they were spotted. With the detection of four extra BBH mergers the researchers find out more about the population of these double stars in deep space and about the occasion rate for these types of coalescences.

The observed BBHs cover a wide variety of part masses, from 7.6 to 50.6 solar masses. The new occasion GW170729 is the most enormous and remote gravitational-wave source ever observed. In this coalescence, which took place approximately 5 billion years earlier, a comparable energy of practically 5 solar masses was transformed into gravitational radiation.

In 2 BBHs (GW151226 and GW170729) it is highly likely that a minimum of one of the combining black holes is spinning. One of the new occasions, GW170818, spotted by the LIGO and Virgo observatories, was extremely exactly determined in the sky. It is the very best localized BBH to date: its position has actually been related to an accuracy of 39 square degrees (195 times the evident size of the moon) in the northern celestial hemisphere.

The clinical documents explaining these new findings provide a brochure of all the gravitational wave detections and prospect occasions of the 2 observing runs in addition to explaining the qualities of the combining black hole population. Most especially, the researchers discover that practically all black holes formed from stars are lighter than 45 times the mass of the Sun.

Panopticonof gravity traps: This illustration reveals the masses of black holes, which were spotted by gravitational waves (blue) and by observations in the electro-magnetic spectrum (purple). In the lower part, the neutron stars can be seen which were likewise signed up in ‘light’ (yellow). The 2 neutron stars that combined in the occasion GW170817, which were spotted by gravitational waves, are illustrated in orange. The numbers on the left show solar masses. © LIGO-Virgo/ Frank Elavsky/ Northwestern

“State-of-the-art waveform models, advanced data processing and better calibration of the instruments, have allowed us to infer astrophysical parameters of previously announced events more accurately”, states Alessandra Buonanno, director of the “Astrophysical and Cosmological Relativity” department at AEI-Potsdam, and College Park teacher at University ofMaryland “I look forward to the next observing run in Spring 2019, where we expect to detect more than one black-hole merger every 15 days of data search!”

“I am happy that many of the advanced detector technologies developed at our GEO600 detector have helped to make the O2 run so sensitive and that in O3 another technology pioneered at GEO600, squeezed light, will be employed in LIGO and Virgo”, states Karsten Danzmann, director of the “Laser Interferometry and Gravitational Wave Astronomy” department at AEI-Hannover

The eleven with confidence spotted gravitational waves were found utilizing 3 independent analyses: 2 various so-called “matched-filter” analyses utilizing relativistic designs of gravitational waves from compact binary coalescences and one unmodeled look for short-duration bursts. In addition to these detections, the researchers provided a set of 14 minimal prospect occasions recognized by the 2 matched-filter analyses.

The 3rd observing run (O3) of Advanced LIGO and Virgo is prepared to begin in early2019 With more level of sensitivity upgrades to both LIGO and Virgo in addition to the potential customers of the Japanese gravitational-wave detector KAGRA signing up with the network perhaps towards completion of O3, numerous 10s of binary observations are expected in the coming years.

In O3, observational notifies activated by gravitational-wave observations will be dispersed openly, permitting all astronomers– beginners and specialists alike– to perform follow-up observations.

New post published on: https://www.livescience.tech/2018/12/10/four-new-sources-of-gravitational-waves/

[eastformsdnb]

25 minutes of dark amen choppage and subsonic bass lines for sci-fi addicts brought by Operator

Tune in for new episodes via SoundCloud, HearThisAt, MixCloud, iTunes, TuneIn & more

Tracklist: Dauntless - Insignificant [Renegade Hardware] Dom & Roland, Fierce, Xanadu - Ultraviolet [Dom & Roland Productions] Apostroph - Tolerate [Renegade Hardware] DJ E - Black Powder [Renegade Hardware] Fanu - Otherworld [Lightless Recordings] Fanu - Everything Is One [Lightless Recordings] Voyage - Extraterrestrial [Tech Itch Recordings] Voyage - GEO600 [Tech Itch Recordings] Voyage - Modified [Tech Itch Recordings] The Clamps - Weltschmerz [Invisible] Dauntless & Sach - Erasure [Invisible] Ulterior Motive - Tech2 [Shogun Audio]

[thepotterpapers]

Harry Potter and the upgrade of GEO600

Harry Potter and the upgrade of GEO600

— Potter Papers (@PotterPapers) July 18, 2019

[aartisenblog]

GET THIS BOOK Author: E. Papantonopoulos Published in: Springer ISBN: 3-540-22712-1 File Type: pdf File Size: 3 MB Language: English Description The Physics of the Early Universe is an edited version of the review talks given in the Second Aegean School on the Early Universe, held in Ermoupolis on Syros Island, Greece, in September 22-30, 2003. The aim of this book is not to present another proceedings volume, but rather an advanced multiauthored textbook which meets the needs of both the postgraduate students and the young researchers, in the field of Physics of the Early Universe. The first part of the book discusses the basic ideas that have shaped our current understanding of the Early Universe. The discovering of the Cosmic Microwave Background (CMB) radiation in the sixties and its subsequent interpretation, the numerous experiments that followed with the enumerable observation data they produced, and the recent all-sky data that was made available by the Wilkinson Microwave Anisotropy Probe (WMAP) satellite, had put the hot big bang model, its inflationary cosmological phase and the generation of large scale structure, on a firm observational footing. An introduction to the Physics of the Early Universe is presented in K. Tamvakis’ contribution. The basic features of the hot Big Bang Model are reviewed in the framework of the fundamental physics involved. Short comings of the standard scenario and open problems are discussed as well as the key ideas for their resolution. It was an old idea that the large scale structure of our Universe might have grown out of small initial fluctuations via gravitational instability. Now we know that matter density fluctuations can grow like the scale factor and then the rapid expansion of the universe during inflation generates the large scale structure of our Universe. R. Durrer’s review offers a systematic treatment of cosmological perturbation theory. After the introduction of gauge invariant variables, the Einstein and conservation equations are written in terms of these variables. The generation of perturbations during inflation is studied. The importance of linear cosmological perturbation theory as a powerful tool to calculate CMB anisotropies and polarisation is explained. The linear anisotropies in the temperature of CMB radiation and its polarization provide a clean picture of fluctuations in the universe after the big bang. These fluctuations are connected to those present in the ultra-high-energy universe, and this makes the CMB anisotropies a powerful tool for constraining the fundamental physics that was responsible for the generation of structure. Late time effects also leave their mark, making the CMB temperature and polarization useful probes of dark energy and the astrophysics of reionization. A. Challinor’s contribution discusses the simple physics that processes primordial perturbations into the linear temperature and polarization anisotropies. The role of the CMB in constraining cosmological parameters is also described, and some of the highlights of the science extracted from recent observations and the implications of this for fundamental physics are reviewed. It is of prime interest to look for possible systematic uncertainties in the observations and their interpretation and also for possible inconsistencies of the standard cosmological model with observational data. This is important because it might lead us to new physics. Deviations from the standard cosmological model are strongly constrained at early times, at energies on the order of 1 MeV. However, cosmological evolution is much less constrained in the post-recombination universe where there is room for deviation from standard Friedmann cosmology and where the more classical tests are relevant. R. Sander’s contribution discusses three of these classical cosmological tests that are independent of the CMB: the angular size distance test, the luminosity distance test and its application to observations of distant supernovae, and the incremental volume test as revealed by faint galaxy number counts. The second part of the book deals with the missing pieces in the cosmological puzzle that the CMB anisotropies, the galaxies rotation curves and microlensing are suggesting: dark matter and dark energy. It also presents new ideas which come from particle physics and string theory which do not conflict with the standard model of the cosmological evolution but give new theoretical alternatives and offer a deeper understanding of the physics involved. Our current understanding of dark matter and dark energy is presented in the review by V. Sahni. The review first focusses on issues pertaining to dark matter including observational evidence for its existence. Then it moves to the discussion of dark energy. The significance of the cosmological constant problem in relation to dark energy is discussed and emphasis is placed upon dynamical dark energy models in which the equation of state is time dependent. These include Quintessence, Braneworld models, Chaplygin gas and Phantom energy. Model independent methods to determine the cosmic equation of state are also discussed. The review ends with a brief discussion of the fate of the universe in dark energy models. The next contribution by A. Lukas provides an introduction into time- dependent phenomena in string theory and their possible applications to cosmology, mainly within the context of string low energy effective theories. A major problem in extracting concrete predictions from string theory is its large vacuum degeneracy. For this reason M-theory (the largest theory that includes all the five string theories) at present, cannot provide a coherent picture of the early universe or make reliable predictions. In this contribution particular emphasis is placed on the relation between string theory and inflation. In an another development of theoretical ideas which come from string theory, the universe could be a higher-dimensional spacetime, with our observable part of the universe being a four-dimensional “brane” surface. In this picture, Standard Model particles and fields are confined to the brane while gravity propagates freely in all dimensions. R. Maartens’ contribution provides a systematic and detailed introduction to these ideas, discussing the geometry, dynamics and perturbations of simple braneworld models for cosmology. The last part of the book deals with a very important physical process which hopefully will give us valuable information about the structure of the Early Universe and the violent processes that followed: the gravitational waves. One of the central predictions of Einsteins’ general theory of relativity is that gravitational waves will be generated as masses are accelerated. Despite decades of effort these ripples in spacetime have still not been observed directly. As several large scale interferometers are beginning to take data at sensitivities where astrophysical sources are predicted, the direct detection of gravitational waves may well be imminent. This would (finally) open the long anticipated gravitational wave window to our Universe. The review by N. Andersson and K. Kokkotas provides an introduction to gravitational radiation. The key concepts required for a discussion of gravitational wave physics are introduced. In particular, the quadrupole formula is applied to the anticipated source for detectors like LIGO, GEO600, EGO and TAMA300: inspiralling compact binaries. The contribution also provides a brief review of high frequency gravitational waves. Over the last decade, advances in computer hardware and numerical algorithms have opened the door to the possibility that simulations of sources of gravitational radiation can produce valuable information of direct relevance to gravitational wave astronomy. Simulations of binary black hole systems involve solving the Einstein equation in full generality. Such a daunting task has been one of the primary goals of the numerical relativity community. The contribution by P. Laguna and D. Shoemaker focusses on the computational modelling of binary black holes. It provides a basic introduction to the subject and is intended for non-experts in the area of numerical relativity. The Second Aegean School on the Early Universe, and consequently this book, became possible with the kind support of many people and organizations. We received financial support from the following sources and this is gratefully acknowledged: National Technical University of Athens, Ministry of the Aegean, Ministry of the Culture, Ministry of National Education, the Eugenides Foundation, Hellenic Atomic Energy Committee, Metropolis of Syros, National Bank of Greece, South Aegean Regional Secretariat. We thank the Municipality of Syros for making available to the Organizing Committee the Cultural Center, and the University of the Aegean for providing technical support. We thank the other members of the Organizing Committee of the School, Alex Kehagias and Nikolas Tracas for all their efforts in resolving many issues that arose in organizing the School. The administrative support of the School was taken up with great care by Mrs. Evelyn Pappa. We acknowledge the help of Mr. Yionnis Theodonis who designed and maintained the webside of the School. We also thank Vasilis Zamarias for assisting us in resolving technical issues in the process of editing The Physics of the Early Universe. Last, but not least, we are grateful to the staff of Springer-Verlag, responsible for the Lecture Notes in Physics, whose abilities and help contributed greatly to the appearance of The Physics of the Early Universe.

[didsbumeare-blog]

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[ca-se-passe-la-haut]

Reprise de la chasse aux ondes gravitationnelles

La chasse aux ondes gravitationnelles vient de reprendre ce lundi 1er avril avec les deux interféromètres américains LIGO et l'européen Virgo, tous les trois remis à niveau pour atteindre des performances encore décuplées, grâce à une technique quantique très particulière. Les détecteurs interférométriques  pourraient maintenant observer une fusion de trous noirs ou d'étoiles à neutrons toutes les semaines...

L'arrêt aura duré 19 mois, une éternité depuis les dernières détections d'ondes gravitationnelles. Les chercheurs sont aujourd'hui très optimistes suite à la mise à niveau qu'ils viennent d'effectuer sur les trois systèmes, avec l'espoir de pouvoir détecter pourquoi pas le signal d'une supernova ou bien la fusion hybride d'une étoile à neutrons avec un trou noir. Cette nouvelle campagne d'observation, qu'on appelle le run O3, va durer près d'un an, jusqu'en mars 2020. Lors des deux premiers runs, LIGO et Virgo ont détecté 11 événements gravitationnels : 10 fusions de trous noirs de quelques dizaines de masses solaires et une fusion de deux étoiles à neutrons. 

Le réseau de détecteurs, avec sa toute nouvelle sensibilité, devrait pouvoir montrer une détection par semaine en moyenne, alors qu'elle était d'environ une par mois dans la version antérieure. Cette amélioration matérielle va en effet permettre de beaucoup mieux séparer le bruit de fond du véritable signal produit par les ondes gravitationnelles. Se faisant, les physiciens auront accès à des informations plus riches sur le processus de fusion à partir de la forme détaillée des ondes gravitationnelles (en temps, fréquence et amplitude). Parmi ces informations additionnelles pourraient se glisser la vitesse de rotation des trous noirs et leur direction relative de rotation l'un par rapport à l'autre, c'est à dire tester leur potentiel alignement. Par exemple, si les axes de rotation des deux trous noirs en coalescence sont parallèles, cela indiquera qu'ils avaient une origine commune et qu'ils avaient débuté leur vie comme deux étoiles d'un même système binaire. Inversement, si les axes sont aléatoires, on pourra en conclure que les deux trous noirs se sont formés indépendamment l'un de l'autre et qu'ils se sont rencontrés sur le tard...

L'interféromètre le plus sensible des trois était celui de LIGO situ�� à Livingston en Louisiane. Pour ce run O3, les physiciens sont encore parvenus a booster sa sensibilité de 40%. Quant à Virgo, les physiciens européens sont parvenus à doubler la distance à laquelle il peut détecter des événements cataclysmiques par leurs ondes gravitationnelles.

Ce saut de sensibilité a été en grande partie obtenu grâce à deux modifications dans les lasers qui sont au cœur des interféromètres : d'une part une augmentation de la puissance des lasers, et d'autre part l'application d'une technique de physique quantique qu'on appelle la "compression de lumière" qui exploite une astuce de la mécanique quantique. L'idée de cette méthode qui a été développée dès le début des années 1990 dans les laboratoires d'optique quantique, est de réduire les fluctuations du vide qui produisent une arrivée aléatoire des photons dans le temps sur le miroir au cours de l'impulsion laser. La compression de lumière permet en quelque sorte de manipuler les fluctuations du vide en décalant certaines d'entre elles vers les basses fréquences et ainsi d'améliorer la détection des plus hautes fréquences.

La méthode avait montré toute sa puissance dès 2010 sur un interféromètre optique utilisé comme détecteur-test de LIGO, le détecteur GEO600 situé près d'Hanovre en Allemagne. L'amélioration de la détection des plus hautes fréquences va booster la détection des objets compacts coalescents de plus faible masse : étoiles à neutrons et trous noirs de quelques masses solaires. La détection des hautes fréquences va surtout permettre de suivre ces relativement petits objets jusqu'au terme de leur processus de fusion, là où ils tournent le plus vite l'un autour de l'autre. L'enjeu est réellement crucial. 

Mais il y a aussi une autre grande nouveauté avec ce troisième run de détection de LIGO et Virgo : les physiciens ont décidé de partager en temps réel les alertes lorsqu'une onde gravitationnelle est détectée, pour permettre à n'importe qui (surtout des professionnels) à observer la zone du ciel incriminée, à la recherche d'une contrepartie électromagnétique (des infra-rouges au rayons gamma). Les chercheurs gravitationnels ont même conçu une application mobile spécifique pour envoyer les alertes très largement. Les astrophysiciens vont ainsi pouvoir se régaler en mode "multimessagers". Il faut se rappeler que dans les deux runs précédents, il n'en avait pas du tout été ainsi : pour pouvoir exploiter les données gravitationnelles, les astrophysiciens des photons ou des neutrinos devaient signer un accord de confidentialité avec LIGO-Virgo pour recevoir les alertes et devaient respecter strictement une période d'embargo avant de pouvoir parler. Cette époque est maintenant révolue. Plus aucune restriction de publications ne sera appliquée. L'astronomie à multimessagers risque de vraiment prendre son envol. 

En parallèle à ses fortes améliorations de LIGO et Virgo, des physiciens japonais sont en train de finaliser leur propre détecteur d'ondes gravitationnelles nommé KAGRA. Ils font aujourd'hui tout leur possible pour que KAGRA puisse être opérationnel avant la fin du run O3, visant le début de l'année 2020. Ce quatrième interféromètre, fonctionnant en coïncidence avec les trois autres, devrait permettre de localiser toujours mieux les sources d'ondes gravitationnelles dans le ciel...

Source

Gravitational-wave hunt restarts — with a quantum boost

Davide Castelvecchi

Nature 568, 16-17 (2019)

http://dx.doi.org/10.1038/d41586-019-01064-2

Illustrations

1) Localisation des 11 événements gravitationnels détectés lors des deux premiers runs par LIGO et LIGO+Virgo (Collaborations LIGO/Virgo)

2) Représentation des fusions de trous noirs et étoiles à neutrons détectés à ce jour en fonction de leur masse (LIGO/Virgo Frank Elavski/ Northwestern University) 

3) Systèmes optiques de test pour appliquer la méthode la compression de lumière (Virgo)

via https://ift.tt/2WFOMCu

[workofcer]

Rainer Weiss, Physicist and Inventor, Shares Insight on Black Holes and Einstein’s Legacy

Albert Einstein’s 1915 theory of general relativity revolutionized how scientists viewed the universe with its geometric portrait of gravity, space and time, and its proposition that certain events in space, like colliding black holes, can cause “ripples” in spacetime called gravitational waves. Einstein’s theory resulted in many researchers attempting to prove the existence of these ripples, and nearly 100 years later, the Laser Interferometer Gravitational-wave Observatory (LIGO) made direct detection of gravitational waves on September 14, 2015. As Rainer Weiss detailed in his lecture last week, the path towards this historic breakthrough has been a long quest in attempting answers to Einstein’s equations and developing the right technology.

Weiss is one of the co-founders of LIGO, which is a joint research facility between the Massachusetts Institute of Technology (MIT) and the California Institute of Technology (CalTech). Weiss is the inventor of the laser interferometer gravitational wave detector, a Professor Emeritus of Physics at MIT, a member of the National Academy of Science, and a fellow of the American Association for the Advancement of Science. In addition to LIGO, Weiss is also a co-founder of NASA’s Cosmic Background Explorer (COBE).

In his lecture, “Gravitational Waves, Black Holes and Einstein’s Legacy,” Weiss traced the technological developments in the field of gravitational wave detection. Weiss demonstrated how Einstein’s complex calculations and the work of other physicists paved the path for LIGO’s success. LIGO not only detected the gravitational waves in 2015, its researchers also determined that these waves originated from the collision of two black holes over one billion years ago, proving the long-held belief of the existence of binary black hole systems.

In addition to LIGO, there are currently detectors all around the world — such as the VIRGO in Italy, the GEO600 in Germany, and the INDIGO in India — and the European Space Agency’s LISA mission will attempt to detect gravitational waves out in space. Weiss emphasized the importance of collaboration between these observatories and detectors for the future of wave detection, especially as researchers continue exploring the universe and its origins.

Originally published at: http://engineering.nyu.edu/news/2016/10/21/rainer-weiss-physicist-inventor-shares-insight-black-holes-einsteins-legacy

[universetoday]

The Future of Gravitational Wave Astronomy: Pulsar Webs, Space Interferometers and Everything

The Future of Gravitational Wave Astronomy: Pulsar Webs, Space Interferometers and Everything

It’s the hot new field in modern astronomy. The recent announcement of the direct detection of gravitational wavesby the Laser Interferometer Gravitational-wave Observatory (LIGO) ushers in a new era of observational astronomy that is completely off the electromagnetic spectrum. This detection occurred on September 15th, 2015 and later earned itself the name GW150914. This occurred shortly after…

[aartisenblog]

GET THIS BOOK Author: E. Papantonopoulos Published in: Springer ISBN: 3-540-22712-1 File Type: pdf File Size: 3 MB Language: English Description The Physics of the Early Universe is an edited version of the review talks given in the Second Aegean School on the Early Universe, held in Ermoupolis on Syros Island, Greece, in September 22-30, 2003. The aim of this book is not to present another proceedings volume, but rather an advanced multiauthored textbook which meets the needs of both the postgraduate students and the young researchers, in the field of Physics of the Early Universe. The first part of the book discusses the basic ideas that have shaped our current understanding of the Early Universe. The discovering of the Cosmic Microwave Background (CMB) radiation in the sixties and its subsequent interpretation, the numerous experiments that followed with the enumerable observation data they produced, and the recent all-sky data that was made available by the Wilkinson Microwave Anisotropy Probe (WMAP) satellite, had put the hot big bang model, its inflationary cosmological phase and the generation of large scale structure, on a firm observational footing. An introduction to the Physics of the Early Universe is presented in K. Tamvakis’ contribution. The basic features of the hot Big Bang Model are reviewed in the framework of the fundamental physics involved. Short comings of the standard scenario and open problems are discussed as well as the key ideas for their resolution. It was an old idea that the large scale structure of our Universe might have grown out of small initial fluctuations via gravitational instability. Now we know that matter density fluctuations can grow like the scale factor and then the rapid expansion of the universe during inflation generates the large scale structure of our Universe. R. Durrer’s review offers a systematic treatment of cosmological perturbation theory. After the introduction of gauge invariant variables, the Einstein and conservation equations are written in terms of these variables. The generation of perturbations during inflation is studied. The importance of linear cosmological perturbation theory as a powerful tool to calculate CMB anisotropies and polarisation is explained. The linear anisotropies in the temperature of CMB radiation and its polarization provide a clean picture of fluctuations in the universe after the big bang. These fluctuations are connected to those present in the ultra-high-energy universe, and this makes the CMB anisotropies a powerful tool for constraining the fundamental physics that was responsible for the generation of structure. Late time effects also leave their mark, making the CMB temperature and polarization useful probes of dark energy and the astrophysics of reionization. A. Challinor’s contribution discusses the simple physics that processes primordial perturbations into the linear temperature and polarization anisotropies. The role of the CMB in constraining cosmological parameters is also described, and some of the highlights of the science extracted from recent observations and the implications of this for fundamental physics are reviewed. It is of prime interest to look for possible systematic uncertainties in the observations and their interpretation and also for possible inconsistencies of the standard cosmological model with observational data. This is important because it might lead us to new physics. Deviations from the standard cosmological model are strongly constrained at early times, at energies on the order of 1 MeV. However, cosmological evolution is much less constrained in the post-recombination universe where there is room for deviation from standard Friedmann cosmology and where the more classical tests are relevant. R. Sander’s contribution discusses three of these classical cosmological tests that are independent of the CMB: the angular size distance test, the luminosity distance test and its application to observations of distant supernovae, and the incremental volume test as revealed by faint galaxy number counts. The second part of the book deals with the missing pieces in the cosmological puzzle that the CMB anisotropies, the galaxies rotation curves and microlensing are suggesting: dark matter and dark energy. It also presents new ideas which come from particle physics and string theory which do not conflict with the standard model of the cosmological evolution but give new theoretical alternatives and offer a deeper understanding of the physics involved. Our current understanding of dark matter and dark energy is presented in the review by V. Sahni. The review first focusses on issues pertaining to dark matter including observational evidence for its existence. Then it moves to the discussion of dark energy. The significance of the cosmological constant problem in relation to dark energy is discussed and emphasis is placed upon dynamical dark energy models in which the equation of state is time dependent. These include Quintessence, Braneworld models, Chaplygin gas and Phantom energy. Model independent methods to determine the cosmic equation of state are also discussed. The review ends with a brief discussion of the fate of the universe in dark energy models. The next contribution by A. Lukas provides an introduction into time- dependent phenomena in string theory and their possible applications to cosmology, mainly within the context of string low energy effective theories. A major problem in extracting concrete predictions from string theory is its large vacuum degeneracy. For this reason M-theory (the largest theory that includes all the five string theories) at present, cannot provide a coherent picture of the early universe or make reliable predictions. In this contribution particular emphasis is placed on the relation between string theory and inflation. In an another development of theoretical ideas which come from string theory, the universe could be a higher-dimensional spacetime, with our observable part of the universe being a four-dimensional “brane” surface. In this picture, Standard Model particles and fields are confined to the brane while gravity propagates freely in all dimensions. R. Maartens’ contribution provides a systematic and detailed introduction to these ideas, discussing the geometry, dynamics and perturbations of simple braneworld models for cosmology. The last part of the book deals with a very important physical process which hopefully will give us valuable information about the structure of the Early Universe and the violent processes that followed: the gravitational waves. One of the central predictions of Einsteins’ general theory of relativity is that gravitational waves will be generated as masses are accelerated. Despite decades of effort these ripples in spacetime have still not been observed directly. As several large scale interferometers are beginning to take data at sensitivities where astrophysical sources are predicted, the direct detection of gravitational waves may well be imminent. This would (finally) open the long anticipated gravitational wave window to our Universe. The review by N. Andersson and K. Kokkotas provides an introduction to gravitational radiation. The key concepts required for a discussion of gravitational wave physics are introduced. In particular, the quadrupole formula is applied to the anticipated source for detectors like LIGO, GEO600, EGO and TAMA300: inspiralling compact binaries. The contribution also provides a brief review of high frequency gravitational waves. Over the last decade, advances in computer hardware and numerical algorithms have opened the door to the possibility that simulations of sources of gravitational radiation can produce valuable information of direct relevance to gravitational wave astronomy. Simulations of binary black hole systems involve solving the Einstein equation in full generality. Such a daunting task has been one of the primary goals of the numerical relativity community. The contribution by P. Laguna and D. Shoemaker focusses on the computational modelling of binary black holes. It provides a basic introduction to the subject and is intended for non-experts in the area of numerical relativity. The Second Aegean School on the Early Universe, and consequently this book, became possible with the kind support of many people and organizations. We received financial support from the following sources and this is gratefully acknowledged: National Technical University of Athens, Ministry of the Aegean, Ministry of the Culture, Ministry of National Education, the Eugenides Foundation, Hellenic Atomic Energy Committee, Metropolis of Syros, National Bank of Greece, South Aegean Regional Secretariat. We thank the Municipality of Syros for making available to the Organizing Committee the Cultural Center, and the University of the Aegean for providing technical support. We thank the other members of the Organizing Committee of the School, Alex Kehagias and Nikolas Tracas for all their efforts in resolving many issues that arose in organizing the School. The administrative support of the School was taken up with great care by Mrs. Evelyn Pappa. We acknowledge the help of Mr. Yionnis Theodonis who designed and maintained the webside of the School. We also thank Vasilis Zamarias for assisting us in resolving technical issues in the process of editing The Physics of the Early Universe. Last, but not least, we are grateful to the staff of Springer-Verlag, responsible for the Lecture Notes in Physics, whose abilities and help contributed greatly to the appearance of The Physics of the Early Universe. https://1.bp.blogspot.com/-E37MId9sYHY/XP1g7zXwDmI/AAAAAAAADr0/1shl66I7L6kw6WKv_-pgel1XhN6BPUwqgCLcBGAs/s400/410r-vlpwXL._SR600%252C315_PIWhiteStrip%252CBottomLeft%252C0%252C35_SCLZZZZZZZ_.jpg

[arxt1]

Gravitational light deflection in Earth-based laser cavity experiments. (arXiv:2002.02170v2 [gr-qc] UPDATED)

As known from Einstein's theory of general relativity, the propagation of light in the presence of a massive object is affected by gravity. In this work, we discuss whether the effect of gravitational light bending can be observed in Earth-based experiments, using high-finesse optical cavities. In order to do this, we theoretically investigate the dynamics of electromagnetic waves in the spacetime of a homogeneous gravitational field and give an analytical expression for the resulting modifications to Gaussian beam propagation. This theoretical framework is used to calculate the intensity profile at the output of a Fabry-P\'erot cavity and to estimate the imprints of Earth's gravity on the cavity output signal. In particular, we found that gravity causes an asymmetry of the output intensity profile. Based on that, we discuss a measurement scheme, that could be realized in facilities like the GEO600 gravitational wave detector and the AEI 10 m detector prototype.

from gr-qc updates on arXiv.org https://ift.tt/2S3TPx2

[arxt1]

Gravitational-wave research as an emerging field in the Max Planck Society. The long roots of GEO600 and of the Albert Einstein Institute. (arXiv:2003.00941v1 [gr-qc])

This chapter will explore the interplay between the renaissance of general relativity and the advent of relativistic astrophysics following German involvement in gravitational-wave research through the window of the Max Planck Society, from the very first interests of its scientists, to the point when gravitational-wave detection became established by the appearance of full-scale detectors and international collaborations. On the background of the spectacular astrophysical discoveries of the 1960s and the growing role of relativistic astrophysics, Ludwig Biermann and his collaborators at the Max Planck Institute for Astrophysics in Munich became deeply involved in research related to such widening horizons, already unveiled by radio astronomy during the 1950s. At the end of the 1960s, Joseph Weber's announcements claiming detection of gravitational waves sparked the decisive entry of this group into the field, in parallel with the appointment of the renowned relativist Juergen Ehlers. The Munich area group of Max Planck institutes provided the fertile ground for acquiring a leading position in the 1970s, facilitating the transition from resonant bars towards laser interferometry and its innovation at increasingly large scales, eventually finding a dedicated site in Hannover in the early 1990s. An early pan-European initiative broke up into two major projects: the British-German GEO600, and the French-Italian Virgo. The German approach emphasized perfecting experimental systems at pilot scales, and never developed into a fully-scaled interferometer, rather joining the LIGO collaboration at the end of the century. In parallel, Ehlers founded an institute for gravitational physics in Potsdam, and soon both branches were unified as the Albert Einstein Institute of the Max Planck Society, one of the central contributors to the detection of gravitational waves in 2015.

from gr-qc updates on arXiv.org https://ift.tt/3aq9VHV